1. Field of the Invention
The present invention relates to a detection mark and a method and an apparatus for detecting a mark. More particularly, the present invention relates to a detection mark which is suitable for a prepaid card such as a passage fee card or a telephone card and a method and an apparatus for detecting such mark.
2. Description of the Related Art
In general, a detection mark is printed on a substrate such as a prepaid card with a black ink. From such detection mark, an information is read by irradiating the black ink mark and detecting variation of reflected light by utilizing a difference of reflectance between a printed part and a non-printed part.
In another method, a detection mark is formed from a phosphor, and an information from the mark is read by selectively detecting an emission emitted from the mark through an optical filter by utilizing a difference of wavelength between the emission and a reflected excitation light from the phosphor (see Japanese Patent Kokai Publication No. 9600/1978).
In a further method, on a printed paper such as a catalog, is printed a mark such as a bar code comprising a photoluminescence layer containing a phosphor which emits light in an infrared wavelength range, whereby informations such as properties and prices of printed materials are easily detected without interfering printed matters (see Japanese Patent Publication Nos. 22326/1979 and 18231/1986).
However, by the method comprising reading the information from the mark by utilizing the reflected light, contaminations or damages of a recorded surface carrying the mark will significantly decrease an intensity of the reflected light, so that the information may be misread.
Though the method comprising reading the informations from the mark by utilizing the emission from the phosphor is resistant to the contaminations of the recorded surface, it is difficult to detect the emission with complete separation from the excitation light since center wavelengths of the emission and the excitation light are very close to each other, so that the reflected light is overlapped over the detected light and a detection accuracy tends to be decreased.
Further, with the bar code comprising the phosphor layer formed on the printed paper, it is known that read errors occur at a high probability.